Practical Architecture Question

Choosing a shard key in InterSystems IRIS for long-term scalability involves the following best practices:

1. Default System-Assigned Shard Key (SASK): Using the RowID as the shard key usually guarantees an even distribution of data and supports efficient parallel data loading and query processing. This approach is often the best for workloads where queries are randomly distributed across the dataset [1][2].

2. Cosharded Joins: If your application performs frequent joins between large tables, using shard keys that enable cosharded joins is critical. Tables that share the same shard key allow local joins within each shard, improving query performance significantly. Equivalent user-defined shard keys (UDSKs) or the use of the COSHARD WITH keyword can ensure this optimization [1][3][2].

3. Unique Constraints: Ensure that unique constraints on sharded tables include the shard key as part of the unique key. Unique constraints that span across shards can severely impact performance [1].

4. Consider Query Patterns: Analyze queries to ensure shard keys align with frequent filter conditions, joins, and group-by operations. This will reduce cross-shard data movement and improve efficiency [1][3].

5. Avoid Sharding Complex Transaction Tables: Tables involved in complex atomic transactions should not be sharded because sharding complicates ensuring atomicity [1].

6. Flexible Schema Design: Plan for scalability by co-sharding related tables or combining sharding with vertical scaling as necessary. InterSystems IRIS also supports hybrid arrangements where application servers work with data shards for distributed computing [4][2].

By adhering to these practices, you reduce the likelihood of encountering performance bottlenecks and avoid requiring major refactoring as your database scales. [1][2]

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